The present invention relates to a liquid crystal projection system and, more particularly, to a projection system adopting reflective type of liquid crystal display.
A prior art transmission-type liquid crystal projection system has the advantages of high image quality, compact size, and portability so that the commercially available reflective type liquid crystal projection system cannot compete with it in compactness, brightness, and price. The main reasons are that optical paths of primary colors between the reflective type liquid crystal display (LCD) panel and the projection lens are too long, and that the required birefringence, stress, and coating characteristics of the prism material are very stringent. Therefore, bad imaging quality will arise, and the brightness is not able to compete with that of a transmission-type liquid crystal projection system.
Accordingly, the present invention proposes a reflective type liquid crystal projection system aimed to resolve the above drawbacks so that the volume of the optical system can be reduced, and the distance of the incident polarized light beam to the reflective type LCD panel can be decreased. Thereby, the imaging quality of the system can be effectively enhanced, and the production cost can be decreased.
The primary object of the present invention is to provide a reflective type liquid crystal projection system having short optical paths and high contrast.
Another object of the present invention is to provide a reflective type liquid crystal projection system, which can resolve the problems encountered in the prior art reflective type LCD technology so as to achieve the effects of good imaging quality, compact size, and low price.
Yet another object of the present invention is to reduce the difficulty of coating the dielectric thin film of the polarizing beam splitter (PBS) used in the reflective type liquid crystal projection system.
According to the present invention, a reflective type liquid crystal projection system comprises an incident light source. A polarization of color-splitting device having a first polarization of color splitter and a second polarization of color splitter is used to let the light beam of one primary color be reflected and the light beam of the other two primary colors penetrate through. The two sets of light beams split by the first polarization of color splitter are reflected by two reflective mirrors, traverse two polarizing plates and a retarder arranged between the reflective mirrors and the second polarization of color splitter, and are then incident on the second polarization of color splitter to penetrate through and be reflected, respectively. The split light beams of three primary colors are assembled into an output light beam by a color-combining device comprising three PBS""s. Finally, the output light beam is projected to form the image via a projection lens.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawings, in which: